Alkylaromatic compounds have been known for many years. They possess good thermal and oxidative stabilities, as disclosed in U.S. Pat. Nos. 4,211,665; 4,238,343; 4,604,491; and 4,714,794. Improvements have been made to the compounds over the years. U.S. Pat. Nos. 5,254,274 and 5,019,670, for example, disclose methods of improving the thermal and oxidative stabilities of PAOs by alkylating unsaturated oligomers with an aromatic compound. The products have improved stability and solvency due to the aromatic component as well as improved rheological characteristics. U.S. Pat. Nos. 4,737,297; 4,714,794; and 4,665,275 disclose various monoalkylate compounds with good oxidative stability and U.S. Pat. No. 5,342,532 discloses a mono- or dialkylate benzothiophene with good oxidative stability. U.S. Pat. No. 5,177,284 discloses making an alkylated naphthalene fluid with improved thermal and oxidative stability using low alkylation temperatures and low acidity zeolite catalysts. U.S. Pat. No. 5,602,086 discloses blends of alkylaromatics with PAOs to improve oxidation stability, solubility, elastomer compatibility, and hydrolytic stability.
Alkylaromatic compounds may be produced by the alkylation of a suitable aromatic compound in the presence of an alkylating agent and an alkylation catalyst such as a Friedel-Krafts catalyst, an acidic clay as described in U.S. Pat. Nos. 4,714,794 and 4,604,491, or a Lewis acid such as aluminum trichloride as described in U.S. Pat. Nos. 4,211,665 and 4,604,491. U.S. Pat. No. 4,570,027 describes the use of a catalyst described as a collapsed silica-alumina zeolite. Various other zeolites may also be used, such as zeolite L, ZSM-4, and ZSM-5 as disclosed in U.S. Pat. No. 4,301,316, zeolite MCM-22 as disclosed in U.S. Pat. No. 5,019,670, or zeolites USY and Beta as described in U.S. Pat. No. 5,177,284.
In current processes to produce alkylaromatic compounds, a residual amount of unreacted aromatic compound and alkylating agent remains in the reactor effluent. It is advantageous to minimize the amount of unreacted material in the reactor effluent to maximize yield of desired product. It is also desirable to minimize the amount of unreacted aromatic compound remaining because industry regulations limit the amount of this material that may be present in finished products. It has been known to apply a batch stripping process to the alkylated compound to strip unreacted aromatic compound from the product. Following this batch stripping process, some amount of unreacted aromatic compound still remains in the product. An improved process to strip further amounts of unreacted aromatic compound from the final product would be advantageous for the reasons cited above.